avformat/cafdec: Check channels

Fixes: signed integer overflow: -1184429040541376544 * 32 cannot be represented in type 'long'
Fixes: 31788/clusterfuzz-testcase-minimized-ffmpeg_dem_CAF_fuzzer-6236746338664448

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/cafdec.c

@@ -79,7 +79,7 @@ static int read_desc_chunk(AVFormatContext *s)
     st->codecpar->channels    = avio_rb32(pb);
     st->codecpar->bits_per_coded_sample = avio_rb32(pb);
 
-    if (caf->bytes_per_packet < 0 || caf->frames_per_packet < 0)
+    if (caf->bytes_per_packet < 0 || caf->frames_per_packet < 0 || st->codecpar->channels < 0)
         return AVERROR_INVALIDDATA;
 
     /* calculate bit rate for constant size packets */